Boron Deficiency Can Limit Soybean Yields – Learn When To Apply

Boron deficiency can be a serious yield-limiting problem in some Arkansas soybean fields. Below is a list of answers to commonly asked questions based on our field observations and research.

Boron deficient soybean (stunted plants and dark leave color) between the previous years rice levees in Poinsett County.
Photo provided by University of Arkansas Soil Fertility Program

How do I know whether I should include boron in my soybean fertilization program?
Boron deficiency has been routinely documented in fields West of Crowley’s Ridge and North of Highway 64. We have also observed boron deficiency in southern Missouri on loamy textured soils that had received a recent lime application, as far South as Palestine (I-40), West into White county, and in a few fields on the East side of Crowley’s Ridge. Most of these fields are usually rotated with rice, have a silt or sandy loam texture, are irrigated with well water, and have (>7.0) high soil pH. Boron fertilization is recommended if you grow soybean on high pH silt or sandy loam soils that are rotated with rice in the area North of Highway 64 and West of Crowley’s Ridge or in other areas where boron deficiency has been diagnosed. Check with your county agent to determine whether boron deficiency has been observed in the area you farm.

When do boron deficiency symptoms appear and what do the look like?
Symptoms of boron deficiency on soybean have been observed from shortly after emergence (V1 stage) through maturity. Boron deficiency is most commonly observed when soil moisture is limited. One of the most common times symptoms are observed is after the first irrigation – plants in some areas of the field respond to irrigation with vigorous growth whereas boron deficient soybean plants will not grow and tend to have darker colored leaves. The importance of soil moisture in boron uptake by plants cannot be stressed enough. The most diagnostic symptom of boron deficiency is death of the growing point. Other symptoms will include misshapen leaves, cupped leaves, short internodes, swollen nodes, and thick leathery leaves.

Photo Captions:

(top) Boron deficient soybean plant with a dead growing point. (bottom) Close-up of healthy soybean leaf (new growth) and boron deficient soybean plants. Note leaf cupping, leathery appearance, and overall dark color of boron deficient plants.
Photos provided by University of Arkansas Soil Fertility Program

What are the best boron fertilization strategies?
There are several options for supplying boron fertilizer to soybean. The first option is to blend granular B (1 lb B/acre) with P and K that will be applied preplant. This option usually works best when the blended fertilizer is applied in advance of planting and incorporated. Granular B may not dissolve when left on top of the soil when rainfall is limited making early application advisable. Boron may also be applied after soybean emergence. For foliar application, early is definitely better than late application. A soluble boron fertilizer or a liquid boron formulation can be mixed with an early herbicide application (check for compatibility before mixing) at rates as low as 0.20 to 0.33 lb B/acre. The amount of foliar burn, which is cosmetic and should not harm yield potential, will increase as the B application rate increases. Boron should be applied by the time soybean begins to bloom (R1 stage). In field trials, where B was yield limiting, waiting until the R1-R2 stage to apply B resulted in a yield loss compared to preplant granular application or foliar application at the V2-V4 stage. Waiting to apply boron until the R1 to R2 stage is risky in that boron deficiency could occur before the boron is applied. The best approach is to apply boron early and go with the most economical and convenient option (granular or soluble) or the one that best fits your management system.

Provided by:
Nathan Slaton, Professor & Director of Soil Testing

University of Arkansas

Division of Agriculture

nslaton@uark.edu - (479) 575-3910